Numerous substrates or structural elements, particularly metallic ones, are coated with an adherent layer of thermoplastic material for protection or insulation having a thickness between about 100 microns and 1 millimeter, and to be able to work, for example to assemble, the coated substrate, it is necessary to remove, at least locally, the layer of thermoplastic material. This layer of plastic material could be mechanically removed, by cutting off and stripping or pushing back but the process now most commonly used is a chemical process by immersing the coated substrate in a hot acid bath. These two techniques are long and difficult to practice, relatively cumbersome, and require skilled personnel.